1. Technical Field of the Invention
The invention relates to a heat exchanger, comprising tubes for a heat exchanger, each tube formed by bending a single plate or stacking two plates, and to communicate with header pipes, and a method of producing the same.
2. Prior Art
A conventionally known heat exchanger comprises a plurality of tubes for making heat exchange of a medium, and header pipes for distributing and collecting the medium, and wherein the tubes are communicatively connected to header pipes.
As shown in FIG. 13, a tube used for such a type of heat exchanger includes a tube 60 which is known being formed by an extrusion molding. This tube 60 is formed into a flat tube by the extrusion molding of an aluminum or aluminum alloy material which is excellent in forming property, and integrally forming partition walls 61 at predetermined intervals in the breadth direction of the tube, to divide a single internal passage 62 into a plurality of passages 62a.
As shown in FIG. 14, it is known that an inner fin type tube 70 is formed by inserting inner fins 71, which are made of another member and have a serpentine cross section, into the tube 70 to divide an inner passage 72 of the tube into a plurality of passages 72a by the inner fins 71.
It is also known to form a metallic plate of aluminum light alloy or the like into a predetermined tube (hereinafter called the tube member) and to braze the tube member as required. This plate is formed by rolling or pressing.
The plate used for such a tube member is generally a brazing sheet having a brazing material claded on its entire surface. Brazing of required parts of the tube member and brazing of other required parts of the heat exchanger are performed by heating an assembled body which was formed into one body by assembling the tube members, header pipes and other parts by means of a jig and the like.
As shown in FIG. 12, for example, a tube member 50' is formed into a predetermined tube by forming beads 51, 51 at appropriate intervals on a strip plate, forming bonding sections 52, 52 at the edges of the plate in its breadth direction, and bending the plate along a bending part 53 at the center in the breadth direction. A plurality of medium passages 54, 54 divided by the beads 51, 51 are formed in the tube. And, the tops of the beads 51, 51 and the opposed inner parts of the tube and the bonding sections 52, 52 are bonded by brazing. The beads can be formed into various shapes such as circular or ellipse depending on uses.
As described above, where a plurality of passages are formed in the tube by the partition walls, inner fins or beads, the inner pressure resistance of the tube itself can be improved, and an appropriate turbulence can be produced in the flow of a heat exchange medium to improve a heat exchange efficiency.
Since the tube 60 formed by the extrusion molding is made of the aluminum or aluminum alloy suitable for the extrusion forming as described above, the fin is often made of a fin material having a brazing material claded in combining the tube and the fin. Where the fin material having the brazing material claded is used to form the fin, a die for forming the fin is abraded heavily, maintenance costs increase, fin material costs increase, and costs in general are increased.
And, the inner fin type tube 70 is needed be produced by separately producing the inner fin 71 and inserting it into the tube 70, resulting in increasing material, fabricating and assembling costs.
On the other hand, the tube member 50' having the beads 51 formed is considered having a lot of advantages in view of production processes, production costs and the like. In this case, the ends of the tube member 50' are inserted into and brazed with the tube holes of the header pipes, and it is required that the joint sections are brazed well to secure the fluid tightness of a medium.
But, since the recesses of the beads 51 at the ends of the tube member 50' form a relatively large gap between the end of the tube member 50' and the tube hole, the brazing becomes defective conventionally, and a ratio of quality products is lowered.
Therefore, the invention described in Japanese Patent Laid-Open Publication No. Hei 4-86489 discloses a tube, which is formed by bending a plate to adhere tightly along the longitudinal direction of the tube to form a bent double-walled projection, so that the leading end face of the projection is contacted with the opposed plate face. Since this tube is formed by bending a plate to adhere tightly to form the double-walled projection, the upper and lower faces of the tube become substantially flat, and the tube can be assembled to the header pipe without forming a gap, so that a problem of brazing property can be remedied.
But, it is hard to uniformly form the double-walled projection, which was formed by bending to tightly adhere the plate, along the longitudinal direction of the tube, and the production process becomes complicated. And, since the top of the double-walled projection formed on the tube is in contact with the plate face, the contact area is reduced, the brazing property is degraded, and the pressure resistance is lowered.
On the other hand, since the beads can be formed uniformly and quickly by rolling, pressing or die forming before or simultaneous with forming the tube, the production process is simple and easy. And, since the bead tops can be bonded to the plate face, the brazing area is increased to improve the brazing property, and the pressure resistance is improved.